CN102918602B - For the method for the reductibility reextraction operational processes spent nuclear fuel without the need to plutonium - Google Patents

Abstract

This invention relates to a method for processing spent nuclear fuel, which, among other advantages, does not require a reductive back-extraction operation of plutonium. The method is particularly suitable for processing uranium oxide fuel as well as mixed uranium and plutonium oxide fuels.

Description

Method for treating spent nuclear fuel in a reductive stripping operation without plutonium

technical field

The present invention relates to a method for reprocessing spent nuclear fuel which, among other advantages, does not require reductive stripping operations of plutonium.

The method finds particular application in the reprocessing of uranium oxide fuel and uranium and plutonium mixed oxide fuel.

Background technique

Currently, plants for reprocessing spent nuclear fuel use the PUREX method (from Plutonium Uranium Refining by EXtraction) to recover the uranium and plutonium present in these fuels.

This is obtained by performing several purification cycles by liquid-liquid extraction. The extractant used is tri-n-butyl phosphate which has a special affinity for uranium and plutonium.

The PUREX method (e.g. carried out at the reprocessing plant (UP2-800, UP3) in La Hague, France) schematically comprises three cycles, namely:

- A first cycle designed to jointly purify uranium and plutonium, separate from fission products and minor amounts of actinides (i.e., americium, curium, and neptunium), distributing uranium and plutonium into two water streams; and

- Two supplementary cycles respectively called "Second Uranium Cycle" and "Second Plutonium Cycle" for purifying uranium and plutonium separately after distribution.

Recently, a major development of the PUREX method called the COEX ^TM method (from combined extraction, COEXtraction) was proposed in International PCT Application Publication No. WO 2007/135178 (Ref. [1]).

While ensuring recovery and purification of uranium and plutonium comparable to the PUREX method, this development could significantly reduce the risk of plutonium being diverted to military use.

It can also produce a stream containing a mixture of purified plutonium, uranium, and optionally neptunium, that is, completely purified from fission products, and use this stream to feed a so-called "co-conversion" unit, which The role of the unit is to prepare mixed oxide (U,Pu)O ₂ or (U,Pu,Np)O ₂ that can be directly used to make MOX type nuclear fuel (from mixed oxide fuel, Mixed OXide Fuel).

For this purpose, the COEX ^TM method provides for the distribution of uranium and plutonium after a purification operation of uranium and plutonium carried out during the first cycle similar to the PUREX method, so as to obtain a first water stream containing plutonium, uranium and optionally neptunium, and a second stream containing uranium and optionally neptunium but not any plutonium.

In all operations downstream of said allocation, it also provides for maintaining plutonium in the presence of uranium and optionally neptunium until mixed oxides (U,Pu)O ₂ or (U,Pu,Np)O ₂ are obtained.

Thus, in the COEX ^TM method, the "second plutonium cycle" of the PUREX method is aimed not at purifying plutonium alone, but at purifying the plutonium, uranium and optionally The cycle of the neptunium mixture is replaced.

In the PUREX and COEX ^TM methods, the partitioning of uranium and plutonium into the two aqueous phases is based on a stripping operation called "reduced" plutonium, since the stripping operation consists of complete reduction of plutonium to oxidation state III (In this oxidation state plutonium is hardly extractable by tri-n-butyl phosphate, and therefore plutonium readily enters the aqueous phase), stripping the plutonium composition from the plutonium-containing organic phase.

For this purpose, an organic phase containing plutonium(IV) is brought into contact with an aqueous nitric acid phase containing a reducing agent capable of reducing said plutonium(IV) to plutonium(III), together with a An anti-nitrous agent for readily formed nitrous acid, thereby stabilizing both the reducing agent and the plutonium(III).

A reductive stripping operation of plutonium is also performed during the steps used to purify plutonium in the PUREX process, and the mixture of plutonium, uranium and optionally neptunium in the COEX ^™ process.

Reductive stripping of these plutonium operations is complicated by combining reduction reactions with liquid-liquid extraction operations due to the occurrence of redox reactions. Effectively, they require the addition of reductants and anti-nitrous acid agents in amounts that can be very substantial for the reprocessing of MOX fuel with high plutonium content, which imposes operational constraints to ensure the stability and safety of these operations ( especially noting certain reaction products).

Furthermore, they require a subsequent operation consisting of reoxidation of plutonium(III) to plutonium(IV), so that the plutonium can be extracted again into the organic phase, or so that it can optionally be preserved in the aqueous phase, since only Plutonium is only stable in aqueous media when it is in oxidation state IV, which complicates the method.

Therefore, due to the prospect of developing new types of plants for the reprocessing of spent nuclear fuel, the inventors set themselves the goal of providing a method, although said method differs from the PUREX and COEX ^TM methods in terms of recovery and purification of uranium and plutonium Same performance, but the method does not require any plutonium reductive stripping operations, specifically to achieve uranium and plutonium partitioning.

They also set themselves the following goals, that with the described method it would be possible to:

- As in the COEX ^TM process, two streams are produced, one containing a mixture of purified plutonium, uranium and optionally neptunium, and the other containing purified uranium,

- or as in the PUREX method, producing two streams, one containing purified plutonium and the other containing purified uranium,

- or produce two streams, one containing a mixture of purified plutonium and neptunium and the other containing purified uranium.

They also set themselves the goal that, if the process is used to produce a stream containing a mixture of purified plutonium, uranium, and optionally neptunium, when adjusting the amount of plutonium and uranium present in the resulting stream It allows a great deal of flexibility when it comes to ratios between.

They also set themselves the goal that the method at least partially uses the knowledge and know-how acquired for the PUREX method, making it possible to apply it on an industrial level in the short or medium term.

Contents of the invention

These and other objectives are achieved with the present invention, which proposes a method for reprocessing spent nuclear fuel comprising at least the following steps:

a) Purification of uranium and plutonium present in the aqueous nitric acid phase obtained by dissolving said fuel in nitric acid to remove americium, curium and most of the fission products also contained in said phase, said purification comprising at least The combined extraction (co-extraction) of uranium in oxidation state VI and plutonium in oxidation state IV into a water-immiscible organic phase containing the first extractant, compared to actinides (III) and fission products, results in The above-mentioned first extractant is more capable of extracting uranium (VI) and plutonium (IV) from the acidic aqueous phase;

b) joint stripping (co-stripping) of the uranium and plutonium co-extracted in step a) into an aqueous nitric acid phase, the uranium being stripped in oxidation state IV and the plutonium in oxidation states IV and VI to thereby During said combined stripping, plutonium(VI) is further formed by disproportionation of plutonium(IV);

c) Partitioning of the uranium and plutonium present in the aqueous nitric acid phase resulting from step b) into a first aqueous phase containing plutonium without uranium or a mixture of uranium and plutonium, and a second aqueous phase containing uranium without plutonium In phase, said distribution includes at least:

- extracting all or part of the uranium in oxidation state VI optionally into an organic phase immiscible with water and comprising a second extraction agent different from the first extraction agent and different from the plutonium (iv) said second extractant is more capable of extracting uranium(VI) from the acidic aqueous phase than that in treating the nitric acid aqueous phase resulting from step b) in order to reduce the plutonium(VI) present in said phase said extraction after and/or in conjunction with plutonium(IV) formation; and

- back extraction of the extracted uranium(VI) into an aqueous nitric acid phase; and

d) Purification of the plutonium or the mixture of uranium and plutonium present in the aqueous phase resulting from the extraction of step c) to remove any fission products that may still be present in said phase.

Thus, in the method of the invention, the partitioning of uranium and plutonium into the two aqueous phases is not based on a stripping operation for reducing the plutonium contained in the organic phase originating from said purification step, but on the basis of the Selective extraction of all or part of the uranium contained in the nitric acid aqueous phase of the combined extraction of uranium and plutonium in the purification step described above.

This is made possible by:

*Firstly, between said purification step and distribution step, a step is carried out, step b), which consists of the combined stripping of uranium and plutonium present in the organic phase originating from said purification step into nitric acid water phase, independent of any reduction reaction composition of plutonium present in said phase; and

*Secondly, in the partitioning step, an organic phase containing an extractant that is more capable of extracting U(VI) from the acidic aqueous phase than Plutonium(IV) is used, thus allowing all All or part of the uranium initially present in the acidic aqueous phase is transferred to the organic phase, leaving the plutonium(IV) in said phase.

In the foregoing and the remainder thereof, it should be understood that when the partition coefficient of uranium(VI) obtained during an extraction operation with said extraction agent is greater than that of plutonium(IV) obtained during the same extraction operation, the same as Said extractant is more capable of extracting uranium(VI) from an acidic aqueous phase than plutonium(IV), independent of the operating conditions under which said extraction is carried out.

Similarly, it should be understood that when the partition coefficient of uranium(VI) and/or plutonium(IV) obtained during an extraction operation with said extraction agent is greater than that of americium, curium and/or fission When the partition coefficient of the product is determined, the extractant is more capable of extracting uranium(VI) and/or plutonium(IV) from the acidic aqueous phase than americium, curium and/or fission products, and compared with the Operating conditions are irrelevant.

In this regard, it may be recalled that in liquid-liquid extraction operations the partition coefficient (denoted D _M ) of the metal element M corresponds to the ratio of its concentration in the organic phase relative to its concentration in the aqueous phase at equilibrium , ie [M] _organic /[M] _water .

Neptunium contained in spent nuclear fuel is found in the aqueous nitric acid phase obtained by dissolving said fuel, mainly in the form of oxidation states V and VI. Considering the similarity in the behavior of uranium (VI) and neptunium (VI) in aqueous and organic solutions, neptunium (VI) is inevitably extracted into the organic phase by the first extractant, and its effect is to make the neptunium (VI) The redox equilibrium that exists between the two oxidation states V and VI shifts towards the formation of neptunium(VI). As a result, step a) combined extraction of uranium and plutonium is accompanied by extraction of neptunium, unless neptunium is provided to be in oxidation state V during or prior to said combined extraction such that it is seldom or impossible to be extracted by said combined extraction Extraction with the first extractant.

On the other hand, by treating the aqueous phase originating from step b) to reduce the plutonium(VI) it contains to plutonium(IV), the redox equilibrium that exists between the oxidation states V and VI of neptunium inevitably The shift towards the formation of neptunium (V) has the effect that little or no neptunium present in the phase can be extracted by the second extractant.

This may advantageously facilitate obtaining an aqueous phase after step d) comprising:

- mixtures of purified plutonium and uranium also containing purified neptunium;

- or purified neptunium-free mixtures of plutonium and uranium;

- or purified plutonium free of uranium and neptunium;

- or purified uranium-free mixtures of plutonium and neptunium.

Therefore in the first preferred embodiment of the method of the present invention, it comprises the following steps at least:

a) purifying the uranium, plutonium and neptunium present in the aqueous nitric acid phase obtained by dissolving the fuel to remove the americium, curium and most of the fission products also contained in said phase, said purging operation comprising at least joint extraction of uranium(VI), plutonium(IV) and neptunium in oxidation state VI into an organic phase comprising said first extractant;

b) Combined stripping of uranium, plutonium and neptunium from step a) into an aqueous nitric acid phase, uranium stripped in oxidation state VI, plutonium stripped in oxidation states IV and VI, and neptunium in oxidation state stripping in oxidation states V and VI;

c) Partitioning of uranium, plutonium and neptunium present in the aqueous nitric acid phase from step b) into a first aqueous phase comprising a mixture of uranium, plutonium and neptunium, and a second aqueous phase comprising uranium without plutonium or neptunium , the allocation operation includes at least:

- selective extraction of a portion of uranium in oxidation state VI into the organic phase comprising said second extractant, after treating the aqueous nitric acid phase resulting from step b) in order to reduce the plutonium(VI) present in said phase performing said extraction operation after forming plutonium(IV); and

- back extraction of the extracted uranium(VI) into an aqueous nitric acid phase; and

d) Purification of the mixture of uranium, plutonium and neptunium present in the aqueous phase resulting from the extraction operation of step c) to remove any fission products that may still be present in said phase.

In this case, step d) preferably includes at least:

- extraction of the mixture of uranium, plutonium and neptunium in oxidation states VI, IV and VI respectively present in the aqueous phase resulting from the extraction operation of step c) into an organic phase immiscible with water and comprising a third extraction agent , the third extractant is different from the second extractant and is more capable of extracting uranium(VI) and plutonium(IV) from the acidic aqueous phase as compared to fission products; and

- Back extraction of the extracted mixture of uranium(VI), plutonium(IV) and neptunium(VI) into the aqueous nitric acid phase.

For this purpose, during the extraction operation of step d), the process according to the invention advantageously comprises treating the aqueous nitric acid phase resulting from the extraction operation of step c), so that the The redox equilibrium shifts towards the formation of neptunium(VI) and thus favors the extraction of neptunium by the third extractant.

In a second preferred embodiment of the method of the invention, it comprises at least the following steps:

a) Purify the uranium and plutonium present in the aqueous nitric acid phase obtained by dissolving the fuel to remove neptunium, americium, curium and most of the fission products also contained in said phase, said purification operation comprising at least the uranium (VI) and plutonium(IV) are co-extracted into the organic phase comprising the first extractant, after treating the aqueous nitric acid phase so as to steer the redox equilibrium existing between the oxidation states V and VI of neptunium towards the formation of neptunium (v) carrying out said co-extraction operation after and/or in conjunction with the transfer;

b) jointly stripping the uranium and plutonium co-extracted in step a) into an aqueous nitric acid phase, the uranium being stripped in the form of oxidation state IV and the plutonium being stripped in the form of oxidation states IV and VI;

c) partitioning the uranium and plutonium present in the aqueous nitric acid phase resulting from step b) into a first aqueous phase comprising a mixture of uranium and plutonium, and into a second aqueous phase comprising uranium without plutonium, said partitioning operation Include at least:

- selective extraction of a portion of uranium in oxidation state VI into the organic phase comprising said second extraction agent, after treating the aqueous phase resulting from step b) in order to reduce the plutonium(VI) present in said phase to plutonium(IV) followed by said extraction operation; and

- back extraction of the extracted uranium(VI) into an aqueous nitric acid phase; and

d) Purification of the mixture of uranium and plutonium present in the aqueous phase resulting from the extraction operation of step c) to remove any fission products that may still be present in said phase.

In this case, step d) preferably includes at least:

- extraction of the mixture of uranium and plutonium in oxidation states VI and IV respectively present in the aqueous phase resulting from the extraction operation of step c) into an organic phase immiscible with water and comprising a third extraction agent, said a third extractant that is different from the second extractant and that is more capable of extracting uranium(VI) and plutonium(IV) from the acidic aqueous phase as compared to fission products; and

- Back extraction of the extracted mixture of uranium(VI) and plutonium(IV) into the aqueous nitric acid phase.

In a third preferred embodiment of the method of the present invention, it comprises at least the following steps:

a) Purify the uranium and plutonium present in the aqueous nitric acid phase obtained by dissolving the fuel to remove neptunium, americium, curium and most of the fission products also contained in said phase, said purification operation comprising at least joint extraction of uranium(VI) and plutonium(IV) into the organic phase comprising the first extractant, after treating the aqueous nitric acid phase so as to steer the redox equilibrium existing between the oxidation states V and VI of neptunium towards the formation of performing said co-extraction after and/or in conjunction with neptunium(V) transfer;

b) joint stripping of the uranium and plutonium co-extracted in step a) into an aqueous nitric acid phase, the uranium being stripped in the form of oxidation state VI and the plutonium being stripped in the form of oxidation states IV and VI,

c) partitioning the uranium and plutonium present in the aqueous nitric acid phase resulting from step b) into a first aqueous phase containing plutonium without uranium, and a second aqueous phase containing uranium without plutonium, the partitioning operation Include at least:

- selective extraction of all uranium in oxidation state VI into the organic phase comprising said second extractant, after treating the aqueous phase resulting from step b) so as to reduce the plutonium(VI) present in said phase to plutonium(IV) followed by said extraction operation; and

- back extraction of the extracted uranium(VI) into an aqueous nitric acid phase; and

d) Purification of the plutonium present in the aqueous phase resulting from the extraction operation of step c) to remove any fission products that may still be present in said phase.

In this case, step d) preferably includes at least:

- extraction of the plutonium in oxidation state IV present in the aqueous phase resulting from the extraction operation of step c) into an organic phase immiscible with water and comprising a third extractant which is in combination with said first The two extractants are different and the third extractant is more capable of extracting plutonium(IV) from the acidic aqueous phase as compared to fission products; and

- Back extraction of the extracted plutonium(IV) into an aqueous nitric acid phase.

In a fourth preferred embodiment of the method of the present invention, it comprises at least the following steps:

a) Purify the uranium, plutonium and neptunium present in the aqueous nitric acid phase obtained by dissolving the fuel to remove the americium, curium and most of the fission products also contained in said phase, said purification operation comprising at least the uranium (VI), plutonium(IV) and neptunium in oxidation state VI are co-extracted into an organic phase comprising said first extractant;

b) Combined stripping of uranium, plutonium and neptunium from step a) into an aqueous nitric acid phase, uranium stripped in oxidation state IV, plutonium stripped in oxidation states IV and VI, and neptunium in oxidation state stripping in oxidation states V and VI;

c) Partitioning of uranium, plutonium and neptunium present in the aqueous nitric acid phase resulting from step b) into a first aqueous phase comprising a mixture of plutonium and neptunium without uranium, and a second aqueous phase comprising uranium without plutonium or neptunium In the aqueous phase, the distribution operation at least includes:

- selective extraction of all uranium in oxidation state VI into the organic phase comprising said second extractant, after treating the aqueous phase resulting from step b) in order to reduce the plutonium(VI) present in said phase to plutonium(IV) followed by said extraction operation; and

- back extraction of the extracted uranium(VI) into an aqueous nitric acid phase; and

d) Purification of the mixture of plutonium and neptunium present in the aqueous phase resulting from the extraction operation of step c) to remove any fission products that may still be present in said phase.

In this case, step d) preferably includes at least:

- extracting the mixture of plutonium and neptunium in oxidation states IV and VI, respectively, present in the aqueous phase resulting from the extraction operation of step c), into an organic phase immiscible with water and comprising a third extractant, said a third extractant that is different from the second extractant and that is more capable of extracting plutonium(IV) from the acidic aqueous phase as compared to fission products; and

- Back extraction of the extracted mixture of plutonium(IV) and neptunium(VI) into the aqueous nitric acid phase.

For this purpose, during the extraction operation of step d), the process of the invention advantageously comprises treating the aqueous nitric acid phase originating from the extraction operation of step c) in order to detoxify the oxidation states present between the oxidation states V and VI of neptunium The reductive equilibrium shifts towards the formation of neptunium(VI).

Irrespective of the embodiment used for the process of the invention, it is preferred to use the same extractant as the first and third extractant, in order to simplify the management of the organic effluents they produce.

The extractant is preferably trialkyl phosphate and still better tri-n-butyl phosphate (or TBP), which is typically hydrogenated with an organic diluent of the hydrocarbon mixture type (specifically as in the PUREX process The proportion of 30% (v/v) in tetrapropylene (TPH)) is used.

However, it is also possible to use two different extractants, as well as to choose the _one of these extractants from the family of N,N-dialkylamides with the general formula RC(O)N(R') One and/or the other, where R is a branched alkyl group at the beta position of the carbonyl, like for example N,N-bis(2-ethylhexyl)-n-butyramide (or DEHBA) or N,N- Bis-(2-ethylhexyl)-3,3-dimethylbutanamide (or DEHDMBA).

The second extractant is preferably selected from N,N-dialkylamides having the same molecular formula as previously described, but wherein R is a branched chain alkyl group at the alpha position of the carbonyl, like for example N,N-di-(2 -ethylhexyl)isobutyramide (or DEHiBA) or N,N-bis-(2-ethylhexyl)-2,2-dimethylpropanamide (or DEHDMPA), with affinity for plutonium(IV) They are known to have a greater affinity for uranium(VI) compared to uranium(VI).

Here again, however, it is possible to choose the second extractant from among trialkyl phosphates with branched alkyl groups, like for example tri-tert-butyl phosphate.

Among the N,N-dialkylamides DEHiBA is particularly preferred because it is particularly selective for uranium(VI) because, for example, in the presence of 3M nitric acid medium (and preferably it ranges in organic diluents from 0.5 mol/L to 2 mol/L, more preferably used from the concentration of 1 mol/L to 1.5 mol/L), the distribution coefficient _DU(VI) and _DPu(IV) obtained using the extractant are respectively 2.7 and 0.03 (ie, a partitioning factor of about 90).

The diluent may be conventionally (randomly) selected from various polar organic diluents or aliphatic organic diluents, the use of which has been proposed for the reprocessing of irradiated nuclear fuel, such as toluene, xylene, t-butylbenzene, tris Cumene, kerosene, dodecane (n-dodecane, hydrogenated tetrapropene, ...), isoparaffins (e.g. Isane IP 185), metanitrobenzotrifluoride and 5,5'-[ Oxy-bis-(methyleneoxy)]bis-(1,1,2,2,3,3,4,4-octafluoropentane).

However, here again for the sake of simplicity in carrying out the process of the invention, it is preferred to use the same diluent as the first and third extractant, so it is a hydrocarbon mixture, such as TPH (if using TBP as the first extractant agent and the third extractant).

Also, irrespective of the embodiment of the method of the invention, the treatment on the aqueous nitric acid phase originating from step b) in order to reduce plutonium(VI) to plutonium(IV) preferably comprises adding nitrous acid to said phase (e.g. , by injecting nitrous acid vapor).

Similarly, in the various previously described embodiments of the present method, the treatment operations used to control the oxidation state of neptunium advantageously include judiciously selective addition of nitrous acid (eg, by injection of nitrous acid vapor).

For example, in the first and fourth embodiments of the method (where, after step d), it is desired to obtain a mixture comprising neptunium, together with uranium and plutonium, or a mixture of only neptunium and plutonium), in step d) Addition of nitrous acid in appropriate amounts (typically, grades 10 ^-4 M to 10 ^-3 M) during the extraction operation can steer the redox equilibrium existing between the oxidation states V and VI of neptunium towards the formation of neptunium (VI ) moves, thereby facilitating its extraction by the third extractant. Said addition is not necessary for the combined extraction operation of step a), empirically it has been shown that at this stage of the process said nitrous acid is present in sufficient amount due to the high activity of the aqueous nitric acid solution being treated.

In the second and third embodiments of the method (where, conversely, after step d) it is desired to obtain a mixture of uranium and plutonium or plutonium alone (without neptunium)), the combined extraction operation at step a) begins Addition of nitrous acid in sufficient amount (typically on the order of 0.01M to 0.1M) before and/or during said co-extraction operation can shift the redox equilibrium existing between the oxidation states V and VI of neptunium towards The neptunium (V) is formed to move, and the neptunium (V) cannot be extracted by the third extractant.

Advantageously, the process of the invention additionally comprises an operation for concentrating the aqueous nitric acid phase resulting from step b) and/or for concentrating the aqueous nitric acid phase resulting from the extraction operation of step c), thereby reducing the The volume of organic phase required for step c) and step d).

Other advantages and characteristics of the present invention will become clear when reading the rest of the description that follows (and it relates to examples of embodiments of the method on an industrial scale).

Apparently, these examples are given only by way of illustrating the invention and not restrictive in any way.

Description of drawings

Figure 1 illustrates a flow diagram of a preferred embodiment of the process of the present invention, firstly designed to produce a mixture of uranium, plutonium and neptunium capable of being converted to mixed oxides (U,Pu,Np)O, and _secondly designed to produce Uranium of sufficient purity for its conversion into _UO2 .

Figure 2 is a flow diagram of a first variant of the embodiment shown in Figure 1, designed to firstly generate a mixture of uranium and plutonium capable of being converted into the mixed oxide (U,Pu) _O2 , and secondly to generate It is converted into _UO2 of sufficiently pure uranium.

Figure 3 is a flow diagram of a second variation of the embodiment shown in Figure 1, designed first to produce plutonium that can be converted to _PuO2 , and secondly to produce uranium that is sufficiently pure for its conversion to _UO2 .

Figure 4 is a flow diagram of a third variation of the embodiment shown in Figure 1, designed firstly to produce a mixture of plutonium and neptunium that can be converted to (Pu,Np) _O2 , and secondly designed to produce Uranium of sufficient purity to be converted into _UO2 .

In these figures, the rectangles mentioned 1-11 represent multi-stage extractors, such as those commonly used for reprocessing spent nuclear fuel (mixer-settlers, pulse columns, centrifugal extractors).

The organic phase entering and leaving these extractors is symbolized by a double line, while the aqueous phase entering and leaving these extractors is symbolized by a single line.

Detailed ways

Reference is first made to Figure 1, which is a flow chart of a preferred embodiment of the method of the present invention, designed to first produce _O2 capable of being converted into mixed oxides (U, Pu, Np) from dissolved liquid (such as _UO2 ) of spent nuclear fuel mixture of uranium, plutonium, and neptunium, and secondarily produces uranium that can be converted into UO ₂ .

This dissolved liquid, obtained by dissolving spent nuclear fuel in concentrated nitric acid (6-10 M) followed by standing the resulting mixture, typically contains 200-300 g/L uranium/2-3 g/L plutonium.

It also contains small amounts of actinides, including neptunium, americium, and curium, and fission products (lanthanum, cerium, praseodymium, neodymium, samarium, europium, yttrium, molybdenum, zirconium, rubidium, ruthenium, palladium, strontium, etc.).

In this embodiment, the method of the invention includes, as a first step, a step for purifying uranium, plutonium and neptunium separately from the actinides (III) (americium and curium) and most fission products, and the The steps described above are preferably performed in the same manner as the purification steps in the PUREX process (e.g. at the UP2-800 plant in La Hague).

Thus, optionally after adjusting the acidity of the dissolved liquid so as to bring the acidity to a value of 4 to 6M, the step comprises:

*A procedure called "Combined U/Pu/Np Extraction" which is intended to be carried out by contacting the liquid with an organic phase containing 30% (v/v) TBP in an organic diluent (eg TPH) and During this period uranium, plutonium and neptunium are jointly extracted from the dissolved liquid due to the redox equilibrium existing between the oxidation states V and VI of neptunium in the aqueous phase shifted towards the formation of neptunium(VI) due to its extraction operation through the organic phase ( Uranium is in oxidation state VI, plutonium is in oxidation state IV, and neptunium is in oxidation state VI), which leads to the extraction of neptunium (if the oxidation reaction kinetics of neptunium(V) is fast enough, the extraction process can be quantitative).

*Operation called "FP scrubbing", which aims to remove fission products from the organic phase originating from the "U/Pu/Np combined extraction" operation, and specifically ruthenium as well as zirconium (during this combined extraction They are extracted by contacting this organic phase with a moderately acidic aqueous nitric acid phase (eg 0.5-3M aqueous nitric acid).

*Operation called "Tc wash" which aims to remove technetium from the organic phase originating from the "FP wash" operation (during "U/Pu/Np co-extraction" by contact with an aqueous nitric acid phase (e.g. 4-5M nitric acid solution) to extract it); and

*Operation called "U/Pu/Np Supplementary Combined Extraction" which aims to partially recover uranium, plutonium and neptunium into the organic phase, followed by "Tc scrubbing" by making this aqueous phase Contacting the organic phase formed by 30% (v/v) TBP in TPH recovered the neptunium into the aqueous phase.

In this way, the four phases obtained are:

Two aqueous phases (or raffinates) derived from the "U/Pu/Np combined extraction" operation and the "U/Pu/Np supplementary combined extraction" operation, one of which contains actinides (III) and various fission products while the other carries technetium and removes them from circulation;

· The organic phase originating from the "U/Pu/Np supplementary extraction" operation, which is sent to the extractor 1 to be added to the organic phase circulating in this extractor; and

• The organic phase originating from the "Tc scrubbing" operation, containing uranium(VI), plutonium(IV), neptunium(VI), and traces of fission products.

The latter organic phase is directed to extractor 5 in which the second step of the process takes place.

The second step (referred to as "U/Pu/Np combined stripping" in Fig. 1) is aimed at the joint stripping of uranium, plutonium and neptunium from the organic phase originating from the "Tc scrubbing" operation without Depends on the reduction reaction of plutonium.

Thus, this step is carried out by contacting the organic phase with an aqueous nitric acid phase (e.g. 0.01-0.05M) with very low acidity when entering reactor 5, but whose acidity increases throughout the operation (e.g. by adding 12M nitric acid ), so that the acidity is on the order of 0.3-0.6M when leaving the extractor 5 so as to prevent the hydrolysis of plutonium.

The aqueous phase can be heated, for example to a temperature of the order of 50° C., in order to reduce the extractability of uranium, plutonium and neptunium by TBP and thereby facilitate the transfer of these elements into the aqueous phase.

At the end of said steps, the following are thus obtained:

• The organic phase which no longer contains any uranium, plutonium, neptunium or fission products and which is directed to a series of extractors (not shown in Figure 1 ) where it is purified for recycling; and

plutonium containing uranium(VI), mostly in oxidation state IV but partly in oxidation state VI (due to the tendency of plutonium(IV) to disproportionate in aqueous media, especially in media that are heated and have a lower acidity so), neptunium(V), neptunium(VI) and an aqueous phase of trace fission products.

The aqueous phase is then concentrated to reduce its volume (eg by evaporation).

It is then subjected to a reduction operation, for example by adding nitrous acid (HNO ₂ ) to the vessel, which is contained before being directed to the extractor 6-8, in which the process is carried out The third step (i.e. the assignment step).

Addition of nitrous acid, for example by injection of nitrous acid vapor, can reduce plutonium(VI) to plutonium(IV) and shift the redox equilibrium existing between the oxidation states V and VI of neptunium towards the formation of neptunium(V), the effect of which is The extractability of plutonium and neptunium is reduced by DEHiBA, which is the extraction agent chosen for the partitioning step, thereby preventing them from following the uranium in the partitioning step.

As can be seen in Figure 1, optionally after adjusting the acidity of the aqueous phase resulting from the reduction operation so that the acidity reaches a value of 4-6M, the distribution step comprises:

*Operation called "U-extraction" which aims at extracting the uranium it contains from said aqueous phase by contacting with an organic phase containing e.g. 0.5-2 mol/L DEHiBA in dodecane (e.g. TPH) Part (VI);

* An operation known as "FP scrubbing", which aims to remove fission products as well as plutonium and neptunium fractions from the organic phase (during "U extraction" by exposing said organic phase to an aqueous phase of moderately acidic nitric acid (e.g. 0.5 -3M) contacts to extract them), and as a precautionary measure, said operation included the addition of nitrous acid to convert neptunium(VI) (due to the possibility of shifting the redox equilibrium existing between the oxidation states V and VI of neptunium, it possibly present in the organic phase) to neptunium (V); and

*Operation called "U wash" which aims to detoxify the organic phase resulting from the "FP wash" operation by contacting the organic phase with an aqueous nitric acid phase of low acidity (eg 0.01-0.03M nitric acid solution). The uranium present in the phase is stripped.

In this case, the aqueous phase can also be heated, for example to a temperature of the order of 50° C., in order to reduce the extractability of uranium by means of DEHiBA and thus facilitate its transfer into the aqueous phase.

In this way, three phases are obtained:

The organic phase originating from the "U scrubbing" operation, which no longer contains uranium, plutonium, neptunium or fission products and which is directed to a series of extractors where it will be purified for recycling (not shown in Figure 1);

the aqueous phase originating from the "U scrubbing" operation, which contains uranium(VI) at a level of purity sufficient to allow it to be considered an end product, capable of being converted to uranium oxide without any additional purification operations, and There is thus circulation of the aqueous phase; and

• Aqueous phase originating from the "U extraction" operation, containing uranium (VI), plutonium (IV) and neptunium (V) and traces of fission products.

The aqueous phase is then concentrated to reduce its volume (eg by evaporation).

After the enrichment, the aqueous phase contains uranium(VI), plutonium mostly in oxidation state IV but partly in oxidation state VI (due to the tendency of plutonium(IV) to disproportionate in the aqueous phase), neptunium(V) and neptunium(VI).

After optional acidification to a value of 4-5M, the phase is directed to extractors 9-11 where the fourth step of the process, ie the purification step, takes place.

As can be seen in Figure 1, the purification steps include:

*Operation called "U/Pu/Np combined extraction" which aims at the joint extraction of uranium(VI), plutonium(IV), plutonium(VI) and neptunium from the aqueous phase originating from said enrichment step , the operation is carried out by contacting the aqueous phase with an organic phase containing 30% (v/v) TBP in TPH, and during this time according to the "U/Pu/Np combination in the purification step The same mechanism involved in "extraction" but quantified as neptunium(VI) by adding nitrous acid in an amount that would allow the catalytic oxidation of neptunium(V) to neptunium(VI) (e.g. by injecting nitrous acid vapor into extractor 9) ground neptunium;

* An operation known as "FP wash" which is intended to extract the organic phase from the organic phase by contacting it with an aqueous nitric acid phase (e.g. Those fission products extracted during the "U/Pu/Np combined extraction" are removed in the phase, but their acidity is increased throughout the operation, for example by adding 12M nitric acid, so that the acidity is between 3M and 5M when leaving the extractor 10 room; and

*Operation called "U/Pu/Np Combined Stripping" which aims at the joint stripping of uranium, plutonium and neptunium from the organic phase originating from said "FP scrubbing", also without relying on plutonium here reduction reaction, and the operation is thus carried out by contacting the organic phase with an aqueous phase having a very low acidity (for example 0.01-0.05M) as it enters the extractor 11, and its acidity increases throughout the operation, The acidity has a grade of 0.3-0.5M when leaving the extractor 11, for example by adding 12M nitric acid.

As previously mentioned, the aqueous phase may be heated, for example to a temperature of the order of 50°C, in order to reduce the extractability of uranium and plutonium by TBP.

In this way, three phases are obtained:

Aqueous phase (or extract) derived from "U/Pu/Np combined extraction" which contains fission products and which is eliminated from circulation;

Organic phase originating from "U/Pu/Np combined stripping" which no longer contains uranium, plutonium, neptunium or fission products and directs said organic phase to a series dedicated to the purification of organic phases containing TBP extractor; and

Aqueous phase derived from "U/Pu/Np combined stripping" containing a mixture of uranium(VI), plutonium(IV), plutonium(VI), neptunium(V) and neptunium(VI) in After optionally adjusting its uranium (VI) content by addition of uranyl nitrate and/or optional storage, it is pure enough for said phase to be sent to be able to convert said mixture into mixed oxides (U, Pu, Np) plant unit of _O2 .

For reasons related to the safe implementation of the inventive method, it is preferably ensured that plutonium is not entrained into the organic phase resulting from the "U/Pu/Np combined stripping" operation carried out in extractors 5 and 11 respectively.

For this purpose it is possible to remove from these organic phases any traces of plutonium they may contain (they most commonly correspond to complexes formed of plutonium and TBP degradation products such as di-n-butyl phosphate) operations (not shown in Figure 1) to accomplish each of these combined stripping operations.

In this case, the operation can consist of the following:

- contacting the organic phase resulting from the aforementioned "U/Pu/Np combined stripping" operation with an aqueous nitric acid phase of low to moderate acidity, e.g. 0.05-2M nitric acid solution containing Plutonium(III) reagents (such as uranium nitrate), and anti-nitrous acid reagents (such as hydrazine);

- or contact these organic phases with an aqueous nitric acid phase also having low to moderate acidity but containing lacunar heteropolyanions and specifically as described in PCT International Application Publication No. WO2005/052950 (ref. [2]) P ₂ W ₁₇ O ₆₁ ^10- , As ₂ W ₁₇ O ₆₁ ^10- , SiW ₁₁ O ₃₉ ^8- , GeW ₁₁ O ₃₉ ^8- or PW ₁₁ O ₃₉ ^7- type heterotungsten salt.

It should also be noted that this type of operation also allows the purification of the organic phase, when available, from the neptunium.

Similar provisions generally do not need to be made for the partitioning step, unless said step is carried out using trialkyl phosphates as extractant, in which case it is advantageous in the "FP wash" operation downstream of said step and the "U reverse Similar operations to those just described (the terms "downstream" and "upstream" are considered here to be associated with the direction of circulation of the organic phase) are performed upstream of the "U stripping" operation to ensure that the aqueous phase originating from the "U stripping" operation Does not contain any traces of plutonium and neptunium.

It should be noted that when reductants (such as uranium nitrate) are used in operations intended only to prevent entrainment of traces of plutonium into the phase, the reductant streams used in these Compared to those required for the stripping of plutonium in the aqueous phase in the secondary cycle, or these streams may be required for stripping operations of the COEX ^™ process. They therefore do not impose the limitations presented above in conjunction with these methods.

Moreover, in order to ensure a stable operation of the method according to the invention, it is also preferable to prevent transporting the extraction agent between steps of the method which do not use the same extraction agent, i.e. between the second and third step and between the third and fourth between steps.

For this purpose, it is possible to make the following provisions:

*Washing of the aqueous phase from the "U/Pu/Np combined stripping" step (shown in Fig. extraction of the extractant into the organic phase; and

* A washing operation of the aqueous phase originating from the "U extraction" operation (shown in Figure 1 ) with TPH in the extractor 6 before concentrating said aqueous phase;

In both cases, it should be borne in mind the fact that subsequent concentration of the washed aqueous phase can remove any remaining traces of extractant entrained and even destroyed by the vapour.

In FIG. 1 , these washing operations using TPH are illustrated by adding TPH upstream of the introduction of the organic phase into extractors 5 and 6 .

As shown in the scheme, the aqueous phase containing the initial product and raffinate can also be subjected to a wash operation with a diluent to reduce the entrainment of extractant in these streams.

Reference is now made to Figure 2 which presents a flow diagram of a first variant of the embodiment shown in Figure 1 which may first produce a mixture of uranium and plutonium capable of being converted into mixed oxides ( _U ,Pu)O , and secondarily produce uranium that can be converted into _UO2 .

This variant differs from the embodiment shown in FIG. 1 in that by adding nitrous acid in such an amount that the redox equilibrium existing between the oxidation states V and VI of neptunium can be shifted towards neptunium (V) (e.g. by adding The injection of nitrous acid vapor into the container containing the dissolved liquid and into said extractor) carries out the combined extraction operation carried out in the extractor 1, thereby preventing its extraction by the TBP of the organic phase.

For this reason, in this variant, the neptunium is not extracted from the dissolved liquid but is eliminated from the circulation together with the actinide (III) immediately after said purification step, and in the absence of neptunium in the purification All operations are performed downstream of the step.

therefore:

- Replacement of the "U/Pu/Np Combined Strip" step shown in Fig. 1 by the so-called "U/Pu Combined Strip" Combined stripping of uranium and plutonium in the organic phase of the "Tc wash" and in the same manner as in the "U/Pu/Np combined stripping" step shown in Figure 1;

- a reduction operation, positioned just before the distribution step shown in Figure 1, which then has only the purpose of reducing the plutonium(VI) contained in the aqueous phase originating from the preceding enrichment operation into plutonium(IV); at the same time

- the operation of the purification step shown in Figure 1 is replaced by the following:

* the operation known as "U/Pu combined extraction", which aims at the joint extraction of uranium(VI), plutonium(IV) and plutonium(VI) from the aqueous phase originating from said enrichment operation;

* an operation known as "FP washing", which aims to remove from said organic phase those fission products extracted during said "U/Pu extraction" operation; and

* An operation called "U/Pu combined stripping", which aims at the joint stripping of uranium, plutonium and plutonium from the organic phase originating from said "FP scrubbing" operation;

These three operations are performed in the same manner as the "U/Pu/Np combined extraction", "FP washing" and "U/Pu/Np combined stripping" operations of the purification steps shown in Figure 1, except that no Any nitrous acid for "U/Pu joint extraction" operation.

In this way, at the end of the "U/Pu combined stripping" operation, an aqueous phase containing a mixture of uranium(VI), plutonium(IV) and plutonium(VI) is obtained, after addition of uranyl nitrate and/or possible After optional storage to optionally adjust its uranium(VI) content, it is pure enough for the phase to be sent to a plant unit capable of converting the mixture into mixed oxides (U,Pu)O ₂ .

Reference is now made to FIG. 3 , which presents a flow diagram of a second variant of the embodiment shown in FIG. 1 , which can produce first plutonium convertible to _PuO2 and secondly uranium convertible to _UO2 .

The variant is different from the embodiment shown in Figure 1 because:

- not only by adding nitrous acid (for example by injecting nitrous acid vapor into the container containing the dissolved liquid and into said extractor) to carry out the combined extraction operation carried out in the extractor 1, thereby removing the neptunium present in said liquid (VI) is reduced to neptunium (V), and thus its extraction is prevented by the TBP of the organic phase,

- Also the "U extraction" operation carried out in the extractor 6 is aimed at extracting all the uranium present in the aqueous phase originating from said reduction operation, it is possible to use a sufficient number of theoretical stages and a sufficient flow of the organic phase.

Thus, for example, for a protocol similar to that given in the example below (where 8 extraction stages (extractor 6) are used and with For 8 washing stages of organic phase flow (extractor 7)), it is sufficient to increase the organic phase (DEHiBA) flow into extractor 6 by 10% (all other parameters being equal) to quantitatively extract uranium and to use An aqueous phase comprising only plutonium is obtained at the output of the extractor.

Therefore, not only are all operations downstream of said purification step carried out without neptunium (as shown in the variant shown in Figure 2), but additionally the one shown in Figure 1 is replaced by Operation of the purification steps:

* the operation known as "Pu extraction", which is intended to extract plutonium(IV) from the aqueous phase resulting from the enrichment operation in question;

* an operation called "FP wash", which aims to remove from said organic phase those fission products extracted during "Pu extraction"; and

* the operation called "Pu scrubbing", which aims to strip plutonium from the organic phase originating from said "FP scrubbing";

These operations were performed in the same manner as the "U/Pu/Np combined extraction", "FP washing" and "U/Pu/Np combined stripping" operations of the purification steps shown in Figure 1, except that " U/Pu extraction" operation.

Thus, after said "Pu stripping" operation step, an aqueous phase comprising plutonium(IV) as well as plutonium(VI) is obtained, after optional storage, for which phase is pure enough to be sent to A plant unit that converts the plutonium into _PuO2 .

Referring now to FIG. 4 , this figure presents a flow diagram of a third variation of the embodiment shown in FIG. 1 , which can first produce plutonium and neptunium that can be converted to (Pu,Np) _O2 , and secondly produce plutonium and neptunium that can be converted to UO ₂ Uranium.

Said variant differs from the embodiment shown in FIG. 1 in that, as in the previous variant, the "U extraction" operation carried out in the extractor 6 is intended to extract the All uranium.

For this reason, the operation of the purification step shown in Figure 1 was replaced by the following:

* the operation known as "Pu/Np combined extraction", which aims at extracting plutonium(IV) and neptunium from the aqueous phase originating from said enrichment operation;

* an operation called "FP wash", which aims to remove from said organic phase those fission products extracted during said "Pu/Np combined extraction"; and

* An operation called "Pu/Np combined stripping", which aims at the joint stripping of plutonium and neptunium from the organic phase originating from said "FP scrubbing" operation;

These operations were carried out in the same manner as the "U/Pu/Np combined extraction", "FP washing" and "U/Pu/Np combined stripping" operations of the purification step shown in FIG. 1 .

In this way, after the described "Pu/Np combined stripping" operation, an aqueous phase containing a mixture of plutonium(IV), plutonium(VI), neptunium(V) and neptunium(VI) is obtained, in optional storage Afterwards, it is sufficient for said phase to be sent to a plant unit capable of converting said mixture into mixed oxides (Pu, Np)O ₂ .

For example, for the embodiment of the method of the invention shown in Figure 1, the simulation was carried out using the PAREX software of COMMISSARIAT AL'ENERGIE ATOMIQUE.

The simulated data are as follows:

Dissolving liquid:

[U]=250g/L

[Pu]=3.02g/L

[Np]=0.24g/L

[HNO ₃ ]=4.5M

Flow rate input to extractor 1 = 637L/h

Purification steps:

*Organic phase entering extractor 1: 30% (v/v) TBP in TPH circulated at a flow rate of 1272 L/h;

*Water phase entering extractor 2: 2M _HNO3 solution circulated at 273L/h flow rate;

*Aqueous phase entering extractor 3: 1.5M _HNO3 aqueous solution circulated at a flow rate of 304L/h, then acidified by adding a 12M _HNO3 solution circulated at a flow rate of 243L/h;

* Organic phase entering extractor 4: 30% (v/v) TBP in TPH circulated at a flow rate of 545 L/h;

Combined stripping of uranium and plutonium:

*Aqueous phase entering extractor 5: 0.01M _HNO3 solution circulated at 2317L/h, then acidified by adding 12M _HNO3 solution circulated at 75L/h; temperature = 50°C;

*Aqueous phase leaving extractor 5: [U]=65g/L; [Pu]=0.78g/L; [Np]=0.062g/L; Pu(VI) present; flow rate=2450L/h;

Assignment steps

*Water phase entering extractor 6: [U]=314g/L; [Pu(IV)]=3.8g/L; [Np]=0.3g/L; [HNO ₃ ]=5M; flow rate=508L/h ;

*Organic phase entering extractor 6: 1.5M%DEHiBA in TPH (v/v) circulated at a flow rate of 1379L/h;

*Water phase entering extractor 7: 1.5M _HNO3 solution circulated at 226L/h flow; add _HNO2 ;

*Water phase entering extractor 8: 0.01M HNO ₃ solution circulated at a flow rate of 735L/h; temperature=50°C;

*Aqueous phase leaving extractor 8: [U]=200g/L;

*Aqueous phase leaving extractor 6: [U]=1.56g/L; [Pu]=2.85g/L; [Np]=0.228g/L; flow rate is 677.7L/h;

Purification steps:

This step is carried out after the concentration operation and acid conditioning of the production stream obtained from the previous steps.

*Water phase entering extractor 9: [U]=23.6g/L; [Pu]=43g/L; [Np]=3.45g/L; [HNO ₃ ]=4.8M; flow rate=44.9L/h;

* Organic phase entering extractor 9: 30% (v/v) TBP in TPH circulated at a flow rate of 60 L/h;

*Aqueous phase entering the extractor 10: 1.5M _HNO3 solution circulating at a flow rate of 12L/h, then acidified by adding a 10M _HNO3 solution circulating at a flow rate of 3L/h;

*Water phase entering extractor 11: 0.01M _HNO3 solution circulated at a flow rate of 66.9L/h, then acidified by adding a 10M _HNO3 solution circulated at a flow rate of 2.1L/h; temperature = 40°C;

*Aqueous phase leaving extractor 11: [U]=15g/L; [Pu]=27.4g/L; [Np]=2.2g/L; [ _HNO3 ]=0.5M; flow=70.6L/h.

In this way, 15g/L uranium, 27.4g/L _plutonium and 2.2g/ The aqueous phase of the mixture of L neptunium.

cited references

[1]WO-A-2007/135178

[2]WO-A-2005/052950

Claims (20)

1., for a method for reprocessing spent nuclear fuel, at least comprise the following steps:

A) uranium existed in the nitric acid aqueous phase by making described fuel dissolution obtain in nitric acid and plutonium are purified, with described mutually in the americium, curium and the most of fission product that also comprise separate, described purification at least comprises the uranium being in oxidation state VI and the plutonium combined extraction that is in oxidation state IV to not miscible with water and comprise in the organic phase of the first extractant, compared with actinide (III) and fission product, described first extractant more can from sour water mutually Extraction of Uranium (VI) and plutonium (IV);

B) by step a) uranium of combined extraction and plutonium combine and be stripped in nitric acid aqueous phase, uranium carries out stripping with the form of oxidation state VI and plutonium carries out stripping with the form of oxidation state IV and VI thus forms plutonium (VI) in described associating in reextraction process further by the disproportionation of plutonium (IV);

C) will step b be come from) described nitric acid aqueous phase in the uranium that exists and plutonium be assigned to comprise plutonium and not uranium-bearing also or comprise first aqueous phase of potpourri of uranium and plutonium, and comprise uranium and not containing in the second aqueous phase of plutonium, described distribution at least comprises:

-all or part of uranium being in oxidation state VI is optionally extracted into water unmixing and comprises in the organic phase of the second extractant, described second extractant is different from described first extractant, and compared with plutonium (IV), described second extractant more can from sour water mutually Extraction of Uranium (VI), come from step b in process) described nitric acid aqueous phase in case by described mutually in the plutonium (VI) that exists be reduced into plutonium (IV) after and/or jointly carry out described extraction with it; And

-extracted uranium (VI) is stripped in nitric acid aqueous phase; And

D) to coming from step c) extraction described aqueous phase in the potpourri of the plutonium that exists or uranium and plutonium carry out purifying with remove may still be present in described mutually in any fission product.

2. method according to claim 1, at least comprises the following steps:

A) uranium, plutonium and the neptunium purification will existed in the described nitric acid aqueous phase obtained by the described fuel of dissolving, with remove described mutually in the americium, curium and the most of fission product that also comprise, described purification at least comprise by uranium (VI), plutonium (IV) and be in oxidation state VI neptunium combined extraction in the organic phase comprising described first extractant;

B) by step, a) uranium of combined extraction, plutonium and neptunium are combined and are stripped in nitric acid aqueous phase, uranium is stripped with the form of oxidation state VI, plutonium is stripped with the form of oxidation state IV and VI, and neptunium is stripped with the form of oxidation state V and VI;

C) will step b be come from) described nitric acid aqueous phase in the uranium, plutonium and the neptunium that exist be assigned to the first aqueous phase of the potpourri comprising uranium, plutonium and neptunium, and comprise uranium and not containing in the second aqueous phase of plutonium or neptunium, described distribution at least comprises:

-by being extracted in the organic phase comprising described second extractant with being in the uranium partial selective of oxidation state VI, come from step b in process) described nitric acid aqueous phase in case by described mutually in exist plutonium (VI) be reduced into plutonium (IV) after carry out described extraction; And

-extracted uranium (VI) is stripped in nitric acid aqueous phase; And

D) to coming from step c) extraction described aqueous phase in the potpourri of uranium, plutonium and neptunium that exists carry out purifying with remove may still be present in described mutually in any fission product.

3. method according to claim 2, wherein steps d) at least comprise:

-will step c be come from) extraction described aqueous phase in the mixture extraction being in oxidation state VI, the uranium of IV and VI, plutonium and neptunium respectively that exists to not miscible with water and comprise in the organic phase of the 3rd extractant, described 3rd extractant is different with described second extractant and compared with fission product, described 3rd extractant more can from sour water mutually Extraction of Uranium (VI) and plutonium (IV); And

-potpourri of extracted uranium (VI), plutonium (IV) and neptunium (VI) is stripped in nitric acid aqueous phase.

4. method according to claim 3, in steps d) extracting operation during, described method comprises coming from step c) the described nitric acid aqueous phase of extraction process for making the redox equilibrium that exists between oxidation state V and the VI of neptunium mobile towards formation neptunium (VI).

5. method according to claim 1, at least comprises the following steps:

A) uranium existed in the described nitric acid aqueous phase obtained by the described fuel of dissolving and plutonium are purified, with remove described mutually in the neptunium, americium, curium and the most of fission product that also comprise, described purification at least comprises by uranium (VI) and plutonium (IV) combined extraction in the organic phase comprising described first extractant, and described combined extraction is after the described nitric acid aqueous phase of process and/or combines the redox equilibrium being used for making to exist between oxidation state V and the VI of neptunium of carrying out with it towards forming neptunium (V) movement;

B) by step a) uranium of combined extraction and plutonium combine and be stripped in nitric acid aqueous phase, uranium carries out stripping with the form of oxidation state VI and plutonium is stripped with the form of oxidation state IV and VI;

C) will step b be come from) described nitric acid aqueous phase in the uranium that exists and plutonium be assigned to the first aqueous phase of the potpourri comprising uranium and plutonium, and comprise uranium and not containing in the second aqueous phase of plutonium, described distribution at least comprises:

-by being extracted in the organic phase comprising described second extractant with being in the uranium partial selective of oxidation state VI, come from step b in process) described aqueous phase in case by described mutually in exist plutonium (VI) be reduced into plutonium (IV) after carry out described extracting operation; And

-extracted uranium (VI) is stripped in nitric acid aqueous phase; And

D) to coming from step c) extraction described aqueous phase in the potpourri of the uranium that exists and plutonium carry out purifying, with remove may still be present in described mutually in any fission product.

6. method according to claim 5, wherein steps d) at least comprise:

-will step c be come from) extraction described aqueous phase in exist be in the uranium of oxidation state VI and IV and the mixture extraction of plutonium respectively to comprising in the organic phase of the 3rd extractant with water unmixing, described 3rd extractant is different with described second extractant and compared with fission product, described 3rd extractant more can from sour water mutually Extraction of Uranium (VI) and plutonium (IV); And

-potpourri of extracted uranium (VI) and plutonium (IV) is stripped in nitric acid aqueous phase.

7. method according to claim 1, at least comprises the following steps:

A) uranium existed in the described nitric acid aqueous phase obtained by the described fuel of dissolving and plutonium are purified, with remove described mutually in the neptunium, americium, curium and the most of fission product that also comprise, described purification at least comprises by uranium (VI) and plutonium (IV) combined extraction in the organic phase comprising described first extractant, and described combined extraction is after the described nitric acid aqueous phase of process and/or combines the redox equilibrium being used for making to exist between oxidation state V and the VI of neptunium of carrying out with it towards forming neptunium (V) movement;

B) by step a) uranium of combined extraction and plutonium combine and be stripped in nitric acid aqueous phase, uranium carries out stripping with the form of oxidation state VI and plutonium is stripped with the form of oxidation state IV and VI;

C) will step b be come from) described nitric acid aqueous phase in the uranium that exists and plutonium be assigned to and comprise plutonium and uranium-free first aqueous phase, and comprise uranium and not containing in the second aqueous phase of plutonium, described distribution at least comprises:

-all uranium being in oxidation state VI is optionally extracted in the organic phase comprising described second extractant, come from step b in process) described aqueous phase in case by described mutually in exist plutonium (VI) be reduced into plutonium (IV) after carry out described extraction; And

-extracted uranium (VI) is stripped in nitric acid aqueous phase; And

D) to coming from step c) extraction described aqueous phase in the plutonium that exists carry out purifying, with remove may still be present in described mutually in any fission product.

8. method according to claim 7, wherein steps d) at least comprise:

-will step c be come from) extraction described aqueous phase in the plutonium being in oxidation state IV that exists be extracted into water unmixing and comprise in the organic phase of the 3rd extractant, described 3rd extractant is different with described second extractant and compared with fission product, described 3rd extractant more can from sour water mutually Extraction of Plutonium (IV); And

-extracted plutonium (IV) is stripped in nitric acid aqueous phase.

9. method according to claim 1, at least comprises the following steps:

A) uranium, plutonium and the neptunium purification will existed in the described nitric acid aqueous phase obtained by the described fuel of dissolving, with remove described mutually in the americium, curium and the most of fission product that also comprise, described purification run at least comprise by uranium (VI), plutonium (IV) and be in oxidation state VI neptunium combined extraction in the organic phase comprising described first extractant;

B) by step, a) uranium of combined extraction, plutonium and neptunium are combined and are stripped in nitric acid aqueous phase, uranium is stripped with the form of oxidation state VI, plutonium is stripped with the form of oxidation state IV and VI, and neptunium is stripped with the form of oxidation state V and VI;

C) will step b be come from) described nitric acid aqueous phase in the uranium, plutonium and the neptunium that exist be assigned to the potpourri and uranium-free first aqueous phase that comprise plutonium and neptunium, and comprise uranium and not containing in the second aqueous phase of plutonium or neptunium, described distribution at least comprises:

-all uranium being in oxidation state VI is optionally extracted in the organic phase comprising described second extractant, come from step b in process) described aqueous phase in case by described mutually in exist plutonium (VI) be reduced into plutonium (IV) after carry out described extraction; And

-extracted uranium (VI) is stripped in nitric acid aqueous phase; And

D) to coming from step c) extraction described aqueous phase in the potpourri of the plutonium that exists and neptunium carry out purifying with remove may still be present in described mutually in any fission product.

10. method according to claim 9, wherein steps d) at least comprise:

-will step c be come from) described aqueous phase in exist be in the plutonium of oxidation state IV and VI and the mixture extraction of neptunium respectively to not miscible with water and comprise in the organic phase of the 3rd extractant, described 3rd extractant is different from described second extractant, and compared with fission product, described 3rd extractant more can from sour water mutually Extraction of Plutonium (IV); And

-potpourri of extracted plutonium (IV) and neptunium (VI) is stripped in nitric acid aqueous phase.

11. methods according to claim 10, in steps d) extraction during, described method comprises process and comes from step c) the described nitric acid aqueous phase of the extraction redox equilibrium that is used for making to exist between oxidation state V and the VI of neptunium mobile towards formation neptunium (VI).

12. methods according to any one of claim 3 to 11, wherein identical extractant is used as first and the 3rd extractant.

13. methods according to claim 12, wherein TRI N BUTYL PHOSPHATE is used as first and the 3rd extractant.

14. methods according to any one of claim 1-11, wherein said second extractant is selected from N, N-dialkyl amide.

15. methods according to claim 14, wherein said second extractant is N, N-bis--(2-ethyl hexyl) isobutyramide.

16. methods according to any one of claim 1-11, wherein step c) comprise nitrous acid to add to come from step b) described nitric acid aqueous phase in.

17. according to claim 4 or method according to claim 11, wherein in steps d) extraction during the process carried out comprise interpolation nitrous acid.

18. methods according to any one of claim 1-11, in step b) and c) between comprise further concentratedly come from step b) described nitric acid aqueous phase.

19. methods according to any one of claim 1-11, in step c) and d) between comprise further concentratedly come from step c) the described nitric acid aqueous phase of extraction.

20. methods according to any one of claim 1-11, wherein said spent nuclear fuel is the oxide fuel of uranium oxide fuel or uranium and plutonium mixing.